1. Field of the Invention
The present invention relates to a transceiver including a circuit board, a receiving antenna and a transmitting antenna. The present invention also relates to an electronic key including such a transceiver.
2. Description of Related Art
A transmitter including an antenna mounted to a printed circuit board has been proposed. According to Japanese Patent No. 3445644 for instance, the antenna has a conductive plate and a wiring pattern. The conductive plate has a U-shaped cross section, and the wiring pattern has such a ring shape that a part of the ring shape is opened and the wiring pattern has ends across the opened part. One end and another end of the conductive plate are electrically connected with the ends of the wiring pattern.
When a current flows in the conductive plate in a thickness direction of the printed circuit board, the transmitter transmits a polarized wave having a polarization plane parallel to the thickness direction of the printed circuit board. When a current flows in the wiring pattern and the conductive plate in a direction parallel to a surface of the printed circuit board, the transmitter transmits a polarized wave having a polarization plane parallel to the surface of the printed circuit board. The transmitter described in Japanese Patent No. 3445644 transmits an electromagnetic wave by combining the two polarized waves whose polarization planes are perpendicular to each other, thereby reducing an influence of multipath in electromagnetic wave transmission.
A radio wave key having the transmitter described in Japanese Patent No. 3445644 has a transmission function and does not have a receiving function. A radio wave key used in a smart entry system however may need to have a receiving function in addition to a transmission function. In a radio wave key used in a smart entry system, a receiving antenna is mounted on a printed circuit board to receive a signal from a vehicle. In this structure, since the receiving antenna and the transmitting antenna are mounted on the circuit board and spaced apart from each other, the printed circuit board becomes enlarged.